The elucidation of the nature and function of multiple isoaccepting tRNA species present in mitochondria from Tetrahymena and rat liver is the main objective of the present proposal. Particularly, coding specificities and genetic origins of individual tRNAs will be studied. Studies contemplated include: (1) A survey of reversed-phase chromatographic patterns of mitochondrial and cytoplasmic tRNAs. (2) tRNA-DNA hybridization of mitochondrial tRNAs with mitochondrial and nuclear DNA. (3) Determination of coding specificities of all tRNA species by tRNA binding to trinucleotide codons with ribosomes. These studies should clarify (1) the extent of coding degeneracy and universality in mitochondria and (2) the degree of involvement of tRNA in nucleo-mitochondrial coordination.